Changes in Urine Specific Gravity and Bioelectrical Impedance Analysis Between Normal-Hydrated and Euhydrated States

Abstract

BACKGROUND: Urine specific gravity (USG) is a simple way to estimate the hydration of an individual that is directly proportional to urine osmolality. Bioelectrical impedance (BIA) is a way to measure % fat, % water, and % lean body mass in an individual. BIA analysis is used frequently as a way to measure hydration status and body percentages accurately. PURPOSE: Our study measured the effects of extra water consumption on USG and BIA. HYPOTHESIS: We predicted that extra water consumption would cause a decrease in USG, a decrease in % body fat as determined by BIA, and increased in both total body water % and % lean mass by BIA. METHODS: Seventeen males and females between 20-22 years of age participated. Each participant came to the lab twice. All subjects were instructed to keep a 1-day diet diary prior to their first visit. At the first visit, subjects provided a urine sample and had BIA performed. They were then randomly divided into two groups: the control group replicated their diet for the second visit, and the other group consumed an extra liter of water in addition to replicating their diet. Urine samples and BIA information were then collected again on the second visit. RESULTS: Extra water consumption was associated with a significant decreased in USG but not changes in BIA measurements. CONCLUSIONS: USG was affected by extra water consumption, but % body water, % fat mass, and % lean mass by BIA were not.